The ability to repair dented sheet metal, typically car body panels, is of economic importance because when repair is possible it is generally more economical than replacement. The problem that must generally be overcome is that the back portion of the panel is inaccessible, and since most dents are inwardly directed, the dent typically must be pulled to be repaired.
Pulling dents may be accomplished in several ways. Early methods involved drilling a small hole and inserting a pulling tool. More recently, welding a metallic stud to the dent and pulling the stud to reduce the dent has become almost a standard method of smoothing a dent. Such studs resemble a small nail having a head portion that is welded to the sheet metal. The nail is first welded in place. Next, a slide hammer or some type of clamp-on pulling tool is used to pull on the nail and re-contour the sheet metal. At the this point, the nail body is typically cut off, leaving the head still welded to the sheet metal. A time-consuming grinding process then removes the nail head. This method of dent pulling has several disadvantages. The primary disadvantage is the time, effort, and different tools that are required for each step. Also, the user is generally limited in the amount of force that can be put on the stud when pulling it outwardly. The limit is generally less than what is desired, and the studs will often break loose, requiring the process to be repeated. Also, the small area of sheet metal actually welded to the stud, combined with the metal weakening stresses associated with welding process, may result in a hole being formed in the sheet metal. Another hazard is a build-up of residue formed in the welding process. Such residue causes a more uneven final surface, and extra work is required to attempt to remove it.
In part to address these concerns, a new generation of dent pullers has been developed. These new dent pullers are not yet so widely used, but have many advantages over the industry standard stud-welded-to-sheet-metal method of dent pulling. The new generation of dent pullers uses a stick, pull, twist technology in which an electrode, larger than a welding stud, is welded to the indentation in the sheet metal panel. In this method, the user first sticks or welds the electrode to the dent. Once the welded connection is made, the handle of the welding unit is pulled in the direction of the electrode, to reduce the indentation. The electrode's attachment to the sheet metal is released by twisting. This process may be repeated very quickly, and therefore is highly productive.
This type of dent puller is more productive and rugged than the earlier described system, but nevertheless still has several flaws. The principle flaw is the danger of higher-voltage alternating current, particularly when compared to the safety of low-voltage direct current. Also, such stick-pull-twist dent pullers are limited by their need for an alternating current outlet. Such outlets are often inconveniently located, and may be totally lacking in some industrial areas that are wired only for higher voltages. Moreover, alternating current welding often tends to leave more residue that direct current welding. Perhaps most importantly, alternating current welding dent pullers tend to be quite expensive.
For the foregoing reasons, there is a need for new dent puller of the stick-pull-twist type that uses direct current, rather than alternating current, and uses battery power, rather than power from an outlet.